v3.0.1 - Vue3

Breaking changes:

• Upgrade from Vue 2 to Vue 3
• The state.checked, state.selected and state.expanded keys are now mandatory
• Move customStyles 'tree' css in a 'style' key (customStyles.tree.style)
• The tree 'row' css must now be in the customStyles.row.style key

Other changes:

• Add typescript
• Add more documentation in code and refactor some functions